An ink-jet printer that squirts drops of ink to print letters and graphics in a dot-matrix format uses a recording head that causes the pressure in the ink cavity to vary by means of a piezoelectric device which produces mechanical deformation upon application of a drive signal. As typically described in U.S. Pat. No. 3,946,398, part of the pressure compartment in this recording head is formed of a diaphragm, to which a piezoelectric substrate shaped in a thin sheet form is attached.
The ink-jet recording head described in the U.S. Pat. No. '398 is operated in such a way that when a drive signal is applied to the piezoelectric device, the ink cavity contracts, whereupon ink is squirted in drops from the nozzle orifice communicating with the ink cavity to form dots on recording paper. Since the piezoelectric device in sheet form is attached to the diaphragm, the pressure compartment must be made large enough to facilitate the operation of attachment. On the other hand, a plurality of nozzle orifices are spaced at very small intervals in order to improve the print quality. Therefore, the pressure compartment and the nozzles must be connected by fluid passage-ways but this only results in a complicated mechanism.
In order to solve those problems, an improved ink-jet printing head has been proposed in, for example, U.S. Pat. No. 4,072,959, and in this printing head a piezoelectric vibrator is positioned in such a way that its tip faces the orifice of each nozzle, with a dynamic pressure being imparted to ink by displacements of the piezoelectric device so that drops of the ink will be squirted from the nozzles. This proposal has the advantage that the fluid passage-ways connecting the pressure compartment and the nozzles are eliminated to achieve structural simplicity. On the other hand, there is a large acoustic impedance mismatch between the piezoelectric vibrator and ink, so the energy produced by the piezoelectric device is not effectively used in drop generation.
In order to solve this problem, EP-A-278590 proposed an ink-jet recording head in which a plurality of passage-ways are formed in one surface of a piezoelectric substrate in a pattern that matches the dot forming region whereas an electrode is provided on the inner surfaces of each passage-way, so that deformation in a shear mode is produced in the walls of the passage-ways to change the capacities of the grooves.
In this recording head, the ink in passage-ways can be directly compressed, so the passage-ways for communicating the ink cavities with the nozzle orifices are eliminated to achieve structural simplicity. Furthermore, the direct compression of the ink cavities offers the advantage of highly efficient drop generation. On the other hand, "nozzle plates" for forming nozzle orifices that insure a stable jet of ink drops must be fixed with an adhesive to the piezoelectric substrate. Then, the area bonded is directly subjected to the expanding and contracting motions of the piezoelectric substrate and this lowers the strength of bonding between the two members. In addition, it is necessary to apply the adhesive to very small areas but this only increases the complexity of the manufacturing process. As a further problem, a step will be formed unavoidably between a groove and the attached nozzle plate and it is difficult to remove air bubbles that are drawn into the groove from the nozzle orifice due to the advancing and retracting motion of the meniscus formed at the nozzle orifice.